A laser bonding is preferred to the conventional wire bonding since the electronic devices become smaller and more sophisticated and the semiconductor packaging technology for protecting semiconductor chips from various external environments such as dust, moisture or electrical/mechanical loads has encountered limitations in making the devices lighter, thinner and smaller by the conventional wire bonding method. The laser bonding is a method in which a semiconductor chip is attached to a circuit pattern on a circuit board or a circuit tape and is bonded using a laser.
Japanese Patent Registration No. 3303832 discloses a laser bonding technique for collectively connecting each electrode of a semiconductor chip to a substrate. According to Japanese Patent No. 3303832, an adsorption head for adsorbing a semiconductor chip is made of glass through which a laser beam is transmitted, and a Peltier element is coupled to the stage. The semiconductor chip is rapidly heated by directly heating the entire semiconductor chip by the laser beam. The substrate is rapidly heated and cooled by the Peltier element coupled to the stage.
U.S. Patent Publication No. 2016/004938 relates to semiconductor chip packaging, and discloses a bonding technique using a laser for connecting a semiconductor chip die to a circuit board. According to U.S. Patent Publication No. 2016/004938, a bump reflow step is disclosed in which a laser beam is directed toward a semiconductor die to volatilize flux and electrically connect a bump to a circuit pattern.
In Korean Patent No. 10-0913579, a device for bonding a driving circuit board such as FPC (Flexible Printed Circuit), TCP (Tape Carrier Package), CBF (Common Block Flexible Printed Circuit), Driver IC (Driver Integrated Circuit) is disclosed. According to Korean Patent No. 10-0913579, a board to be bonded with a driving circuit board is transferred to and from a bonding operation position to be bonded with the driving circuit board, thereby reducing a tact time and speeding up the operation.
In general, a reflow apparatus is used for attaching a device including an electronic component such as a semiconductor chip or integrated circuit (IC), a transistor (TR), a resistance element (R), and a capacitor (C) to a printed circuit board. Currently, the reflow apparatus may be classified into mass reflow type and laser reflow type.
A mass reflow apparatus mounts a plurality of substrates with solder material such as solder balls, solder pads, or solder paste on the conveyor belt and drives the conveyor belt. The substrate is passed along the conveyor belt through a heating zone equipped with an infrared or ceramic heater. The infrared heaters are provided on the upper and lower sides of the conveyor belt to apply heat to the solder material on the substrate to attach the semiconductor elements thereto.
According to the mass reflow apparatus, the electronic component or device is subject to thermal stress for about 210 seconds at a high temperature of about 50° C. or up to 230 to 290° C. Accordingly, there is a problem that the electronic component or device may be damaged by heat, thereby deteriorating the characteristics or lifetime of the electronic component or device. In addition, there is a problem that it takes a long time of about 3 to 10 minutes for the infrared heater to heat the solder material to bond the electronic component or device to the substrate, which is not economical. In addition, the mass reflow process may cause defects by applying heat to all components on the substrate including the ones that are susceptible to heat, and cause thermal deformation on the overall substrate since heat is applied to the entire substrate.
Meanwhile, automotive headlights have recently been replaced by LEDs. The structures of the substrate for LED headlight vary from two-dimensional to three-dimensional shapes. In the case of an irregular substrate such as a step-shaped or a bowl-shaped substrate on which the LED is mounted, when the LED is bonded to the irregular substrate through the mass reflow process the heat energy is unevenly distributed on the substrate to cause bonding defects, and thermal energy is applied to the substrate as a whole thereby increasing the possibility that thermal deformation may occur throughout the entire substrate.
In addition to automobile headlights, it is difficult to avoid disadvantages of the mass reflow process when the shape of the substrate for bonding semiconductor chips is three-dimensional or irregular.
Therefore, when the substrate is three-dimensional or irregular a laser reflow technique can be a very useful solution. The laser reflow technique is capable of irradiating a homogenized laser beam for each bonding site and easily adjusting each irradiation region of the laser beam.
Nevertheless, the laser reflow technique so far has only been applied to substrates having a generally planar shape, such as PCBs and glass substrates used in devices such as mobile phones and TVs. If the substrate is not provided in a planar form, or if the locations where the semiconductor element is attached are totally irregular, the conventional laser bonding apparatus cannot operate on such substrate.
Accordingly, there is a need for a new laser bonding apparatus and method that can effectively bond electronic components or elements to any shape of three-dimensional structures including automotive tail lamps or headlamps as shown in FIG. 1.